The present invention relates to a spectrally sensitized silver halide photographic emulsion and a photographic light-sensitive material using the emulsion.
A great deal of effort has heretofore been made for attaining higher sensitivity of silver halide photographic light-sensitive materials. In a silver halide photographic emulsion, a sensitizing dye adsorbed to the surface of a silver halide grain absorbs light entered into a light-sensitive material and transmits the light energy to the silver halide grain, whereby sensitivity can be obtained. Accordingly, in the spectral sensitization of silver halide, it is considered that the light energy transmitted to silver halide can be increased by increasing the light absorption factor per the unit grain surface area of a silver halide grain and thereby the spectral sensitivity can be elevated. The light absorption factor on the surface of a silver halide grain may be improved by increasing the amount of a spectral sensitizing dye adsorbed per the unit grain surface area.
However, the amount of a sensitizing dye adsorbed to the surface of a silver halide grain is limited and the dye chromophore cannot be adsorbed in excess of the single layer saturation adsorption (namely, one layer adsorption). Therefore, individual silver halide grains currently have a low absorption factor in terms of the quantum of incident light in the spectral sensitization region.
To solve these problems, the following methods have been proposed.
In Photographic Science and Engineering, Vol. 20, No. 3, page 97 (1976), P. B. Gilman, Jr. et al. disclose a technique where a cationic dye is adsorbed to the first layer and an anionic dye is adsorbed to the second layer using the electrostatic force.
In U.S. Pat. No. 3,622,316, G. B. Bird et al. disclose a technique where a plurality of dyes are adsorbed in multiple layers to silver halide and the Forster-type excitation energy transfer is allowed to contribute to the sensitization.
In JP-A-63-138341 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and JP-A-64-84244, Sugimoto et al. disclose a technique of performing the spectral sensitization using the energy transfer from a light-emitting dye.
In Photographic Science and Engineering, Vol. 27, No. 2, page 59 (1983), R. Steiger et al. disclose a technique of performing the spectral sensitization using the energy transfer from a gelatin-substituted cyanine dye.
In JP-A-61-251842, Ikegawa et al. disclose a technique of performing the spectral sensitization using the energy transfer from a cyclodextrin-substituted dye.
With respect to the so-called linked dye having two separate chromophores which are not conjugated but linked through a covalent bond, examples thereof are described in U.S. Pat. Nos. 2,393,351, 2,425,772, 2,518,732, 2,521,944 and 2,592,196 and European Patent 565,083. However, these are not used for the purpose of improving the light absorption factor. In U.S. Pat. Nos. 3,622,317 and 3,976,493 having an object of improving the light absorption factor, G. B. Bird, A. L. Borror et al. disclose a technique where a linked sensitizing dye molecule having a plurality of cyanine chromophores is adsorbed to increase the light absorption factor and the energy transfer is allowed to contribute to the sensitization. In JP-A-64-91134, Ukai, Okazaki and Sugimoto disclose a technique of bonding at least one substantially non-adsorptive dye such as cyanine dye, merocyanine dye and hemicyanine dye containing at least two sulfo and/or carboxyl groups to a spectral sensitizing dye which can adsorb to silver halide.
In JP-A-6-57235, L. C. Vishwakarma discloses a method of synthesizing a linked dye by a dehydrating condensation reaction of two dyes. Furthermore, in JP-A-6-27578, it is disclosed that the linked dye of monomethinecyanine and pentamethineoxonol has red sensitivity. However, in this case, the light emission of oxonol and the absorption of cyanine do not overlap and the spectral sensitization using the Forster-type excitation energy transfer does not occur, failing in attaining higher sensitivity owing to the light-gathering action of oxonol linked.
In European Patent Publication 887700A1, R. L. Parton et al. disclose a linked dye with a specific linking group.
In U.S. Pat. No. 4,950,587, M. R. Roberts et al. describe spectral sensitization by a cyanine dye polymer.
In this way, a large number of investigations have been made until now for improving the light absorption factor, however, a sufficiently high effect cannot be attained on the improvement of light absorption factor and also a sufficiently high sensitivity cannot be achieved.
Particularly in color light-sensitive materials, the spectral sensitivity must be rendered to fall within an objective wavelength region. The spectral sensitization of a silver halide light-sensitive material usually does not use the absorption of sensitizing dye in the monomer state but uses the J-band formed when the dye is adsorbed to the surface of a silver halide grain. The J-band is very useful for laying the light absorption and the spectral sensitivity in a desired wavelength region because it has absorption acutely shifted to the longer wavelength side than that in the monomer state. In this meaning, even if a sensitizing dye is adsorbed in multiple layers to the grain surface and thereby the light absorption factor can be increased, when the dye indirectly adsorbed to a silver halide grain, namely, dye in the second or subsequent layer is adsorbed in the monomer state, the absorption extends over a very wide range and this is improper as a spectral sensitivity of actual light-sensitive materials.
On the other hand, each color sensitization region has a width of about 100 nm and it is disadvantageous to cause unnecessarily large difference in the sensitivity to light in that range.
Under these circumstances, a technique of adsorbing a sensitizing dye in multiple layers to the surface of a silver halide grain is being demanded, which can satisfy the requirements that the light absorption integrated intensity per the unit grain surface area is increased, the absorption and the spectral sensitivity are limited to a desired color sensitization region, and at the same time the change in the spectral absorption factor and sensitivity with respect to the light in that region is reduced as much as possible.
Furthermore, it has been found that when a sensitizing dye is adsorbed in multiple layers to the grain surface, the amount of gelatin adsorbed decreases, as a result, the protective colloid function is diminished and the grains are readily coagulated in some cases. Accordingly, a technique of adsorbing a sensitizing dye in multiple layers while preventing occurrence of coagulation of grains is being demanded.
One object of the present invention is to provide a silver halide photographic emulsion prevented from coagulation of grains and having high sensitivity.
Another object of the present invention is to provide a photographic light-sensitive material using the emulsion.
These objects have been attained by the following means.
(1) A silver halide photographic emulsion comprising a silver halide grain having a spectral absorption maximum wavelength of less than 500 nm and a light absorption intensity of 60 or more or having a spectral absorption maximum wavelength of 500 nm or more and a light absorption intensity of 100 or more, wherein assuming that the maximum value of spectral absorption factor of the emulsion by a sensitizing dye is Amax, the distance between the shortest wavelength showing 80% of Amax and the longest wavelength showing 80% of Amax is 20 nm or more and the distance between the shortest wavelength showing 50% of Amax and the longest wavelength showing 50% of Amax is 120 nm or less.
(2) A silver halide photographic emulsion comprising a silver halide grain having a spectral absorption maximum wavelength of less than 500 nm and a light absorption intensity of 60 or more or having a spectral absorption maximum wavelength of 500 nm or more and a light absorption intensity of 100 or more, wherein assuming that the maximum value of spectral sensitivity of the emulsion by a sensitizing dye is Smax, the distance between the shortest wavelength showing 80% of Smax and the longest wavelength showing 80% of Smax is 20 nm or more and the distance between the shortest wavelength showing 50% of Smax and the longest wavelength showing 50% of Smax is 120 nm or less.
(3) The silver halide photographic emulsion as described in (1), wherein the longest wavelength showing a spectral absorption factor of 50% of Amax lies in the region of from 460 to 510 nm, from 560 to 610 nm, or from 640 to 730 nm.
(4) The silver halide photographic emulsion as described in (2), wherein the longest wavelength showing a spectral sensitivity of 50% of Smax lies in the region of from 460 to 510 nm, from 560 to 610 nm, or from 640 to 730 nm.
(5) The silver halide photographic emulsion as described in any one of (1), (2), (3) or (4), wherein the silver halide emulsion contains a dye having at least one aromatic group.
(6) The silver halide photographic emulsion as described in any one of (1) to (5), wherein a sensitizing dye is adsorbed in multiple layers onto a silver halide grain, the second sensitizing dye layer has a structure different from the first sensitizing dye layer, and the second sensitizing dye layer contains both a cationic dye and an anionic dye.
(7) The silver halide photographic emulsion as described in any one of (1) to (5), which contains a sensitizing dye having a basic nucleus formed by the condensation of three or more rings.
(8) The silver halide photographic emulsion as described in any one of (1) to (7), wherein the silver halide grain having a spectral absorption maximum wavelength of less than 500 nm and a light absorption intensity of 60 or more or having a spectral absorption maximum wavelength of 500 nm or more and a light absorption intensity of 100 or more is a tabular grain having an aspect ratio of 2 or more.
(9) The silver halide photographic emulsion as described in any one of (1) to (8), wherein the silver halide grain having a spectral absorption maximum wavelength of less than 500 nm and a light absorption intensity of 60 or more or having a spectral absorption maximum wavelength of 500 nm or more and a light absorption intensity of 100 or more is subjected to selenium sensitization.
(10) A silver halide photographic light-sensitive material comprising at least one silver halide photographic emulsion, which contains a silver halide photographic emulsion described in any one of (1) to (9).